I bought a 'Rain Collector Speedy fit water butt filter for circular downpipes'. To have a water butt, we needed to fit a rain water diverter to a cast iron, small diameter downpipe that vanished into the ground at the base. This was the only solution I could find and, at first, I hesitated to pay the price. However, you certainly get what you pay for. It arrived quickly. The instructions are clear and there is a helpful video online. The hole-cutting bit included in the kit worked, although getting through the cast iron pipe was difficult and took ages, even with a plug-in drill. It was good that the part that went into the downpipe could be cut down for a smaller-diameter pipe, like ours. I waited until there had been enough rain to test it before writing this review. The water butt fills well and the diverter switched fine once the water butt was full. It's a great product.